[[CHORE]] Revert "Add codes to errors generated by quit()"

JSHint's emission of the `code` property of errors from the internal
`quit` function is derived from code first contributed by Nikolay S.
Frantsev <privatbank@frantsev.ru>. That contributor could not be reached
to sign JSHint's Contributor License Agreement. Revert their
contribution to the application logic (preserving the corresponding
MIT-licensed test code) so that it may be re-written under the terms of
the Contributor License Agreement.

Revert the changes introduced by
537dcbd

src/jshint.js

@@ -365,7 +365,6 @@ var JSHINT = (function() {
       character: token.from,
       message: message + " (" + percentage + "% scanned).",
       raw: message,
-      code: code,
       a: a,
       b: b
     };
@@ -6526,7 +6525,6 @@ var JSHINT = (function() {
         JSHINT.errors.push({
           scope     : "(main)",
           raw       : err.raw,
-          code      : err.code,
           reason    : err.reason,
           line      : err.line || nt.line,
           character : err.character || nt.from